1. Field of the Invention
The present invention relates to a video signal processing apparatus, and more particularly, to a horizontal/vertical scanning frequency converting apparatus in an MPEG decoding block for converting a method of scanning a decoded signal using an MPEG algorithm without adding an additional motion detecting memory in a decoding process.
2. Description of the Related Art
In general, the compression of a video signal by an MPEG standard is performed by a spacial correlation and a temporal correlation between frames using a variable length code according to the generation probability of a code.
A forward prediction from a past reproduced image and a backward prediction from a future reproduced image are performed together using a frame memory or a field memory in a signal processing operation for compressing the video signal by the MPEG standard.
Three types of images, i.e., an I picture, a P picture, and a B picture are defined in the MPEG standard in order to realize such a bidirectional prediction.
The I picture, the P picture, and the B picture respectively refer to an intra-encoded image (an image encoded using information of one frame), a predictive encoded image (an image encoded using inter-frame forward prediction), and a bidirectionally predictive encoded image (an image encoded using bidirectional prediction).
Processes of restoring a compressed image signal according to a conventional technology will be described in detail with reference to FIG. 1.
As shown in FIG. 3, data is input to a decoding block 1000a (FIG. 1) in the order of an I picture, a P picture, a B picture, and another B picture. Data is output from the decoding block 1000a in the order of the I picture (screen #1), the B picture (screen #2), the B picture (screen #3), and the P picture (screen #4).
Accordingly, a reverse discrete cosine transformed I picture is stored in a first prediction memory 105 by a reverse DCT unit 102 of the decoding block 1000a. When forward error data with respect to the P picture is output from the reverse DCT unit 102, the data of the I picture stored in the first prediction memory 105 is output through a third switching unit 109. The output data is applied to a mixer 103 through a second switching unit 108 and is stored in a second prediction memory 106 after the forward error data is added thereto.
When bidirectional error data with respect to the B picture is output, the data of the I picture and the P picture stored in the first and second prediction memories 105 and 106 are calculated by a mean operator 107 and applied to the mixer 103. The bidirectional error data is added to the calculated data. Then, the addition result is output through the third switching unit 109.
The I picture is generated by self-data without prior or posterior screen information. The P picture is generated by adding mean differential information of the I picture or the P picture two screens prior to the forward error data. The B pictures obtained by inserting two screens between the I (or P) picture and the P picture are generated by adding the differential information of the first previous I (or P) picture, the operation value from the next P picture, and the bidirectional error data to each other.
In general, the flicker and resolution of a screen are improved by doubling the horizontal or vertical frequency in processing a digital video signal.
In order to double the horizontal or vertical scanning frequency of a screen, the restored signal should be progressive scan converted or double scan converted by a three dimensional processing block 1000b. Since it is necessary to additionally provide a signal interpolating memory 111 and a motion detecting memory 112 for this, material expenses increase. Partial deterioration of picture quality occurs during the interpolation of a signal according to motion information and due to the restriction on the capacity of a memory.